| Hand in WED Correlation (thinking): p. 112, 4.36 and 4.37 Applet explorations p. 112, 4.34 and 4.35 correlation meaning 4.26 date heights again You
graphed this by
hand. r = .5653. Now answer the questions. A. If women always married men who were exactly two years older than themselves, what would be the correlation between the ages of husband and wife? (Hint: make a data table and the corresponding scatterplot for 4 or 5 couples with different x's, and look at it.) Correlation (computing & thinking) (This problem looks forward to Ch. 5, sort of) p. 110, 4.28 corn plant density. (SPSS) Notice how the data is entered for SPSS--not as displayed here! but with the first column giving Plants per acre and the second giving Yield. Make a scatterplot. Use your calculator to find the mean yields, and write these on your paper. (Or You can find means for the separate groups in SPSS : in Explore, Plants to the Factor list). Graph the means by hand with a pencil on your printed plot, and connect the means dots. Regression: Postpone Regression C. Use the SPSS Scatterplot handout and graph the regression line for govsal on avgpay (as shown, back page), also the lines for the 4 separate groups (either on one graph or on panels.) Print them out and keep them. Start answering questions 6-11, on p. 3 of the handout. Keep till you can answer all questions. |
Read, to
discuss p. 112, 4.33 Do a rough sketch for yourself. Look at all the graphs you make, and guesstimate the correlation coefficient (before you read or calculate it.) Postpone Regression: Use http://www.whfreeman.com/bps4e, Correlation and Regression applet . p. 148, 5.55 |
Optional
Correlation: Use http://www.whfreeman.com/bps4e, Correlation and Regression applet (see Day 13 for details) to make different scatterplot patterns, and observe their r's. 4.28, I said to
draw the line by hand.
|
Handout (optional) Normal "tables" using
SPSS, creating new variables from old with formulas.
Homework questions?
Relationships: (BPS4e, Ch. 4) Day
12
Timeplots: are scatterplots, where the x axis shows time.
(often
a lurking variable: plot data against order of taking
observations)
Handout on SPSS Scatterplots etc.
pp.1-3,
p.4
, showing subgroups, labeling individual points.
govsal_vs_pay.sav
is the file used for most of the handout. (In SPSS for Class BPS
folder)
Correlation Day 13
Formula yhat = a + b x. Govsal = a
+
b avgpay
To predict
or
estimate a y-value for a given x-value, plug the x value into
the
formula and calculate.
To do it graphically, use the Up-and-Over method (Fig. 5.1, p.116):
Find the x, go straight up to the line, then go over to the y-axis;
that
y-value is the predicted y.
a is y-intercept.
b is slope:
If x increases one unit, yhat increases b
units.
If you know that yhat increases 12 units for every one that x
increases, you know that the slope of the line b = 12.
(In a straight-line relationship, the amount that y increases
for one unit increase in x is the same no matter what value of
x
you start with) RegressionSlope.xls
or
in ClassMaterial\Math151-BPS4e \RegressionDemos Excel BPS4e
We all get the same line from a batch of data because we use the "least-squares best fit" criterion (p. 119): we'll investigate this more closely later.
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